Gross floor area
According to DIN 277, the gross floor area (GFA) of a building is the total of usable surface areas of all floor plan levels and their constructive enclosure. It is therefore measured according to the external dimensions of a building.1
GFA is used in cost calculation in construction in accordance with DIN 276, and in the building replacement cost (NHK 2000/2010) for the valuation and comparison of buildings.2
The gross floor area is often incorrectly confused or equated with the (gross) floor space.3 In accordance with section 20 BauNVO, floor space is calculated by the external dimensions of the building on all floors. Secondary structures, balconies, loggias, terraces and building structures are not taken into account.4
The gross floor area is divided into the net floor area and the construction floor area. The net floor area (NFA) includes the area of usable areas of all floor plan levels located between rising components of the building. It is divided into the usable area (UA), functional area (FA) and circulation area (CA). Furthermore, the net floor area also includes the areas of exposed installations or permanently installed objects (e.g. an oven).
The construction floor area (CFA) is the total of the areas of the rising components of all floor plan levels. These include walls, columns, chimneys, alcoves, wall openings, windows, doors, etc.5
Thus, the GFA can simplistically be described as follows:
GFA = NFA + CFA
NFA = UA + FA + CA6
The areas of buildings are calculated separately according to the classification to the following three categories:
Category a): “Covered and fully enclosed on all sides.” This includes the areas of the cellar, ground floor, upper floor, attic.
Category b): “Covered but not fully enclosed on all sides.” This includes passages, covered balconies or loggias.
Category c): “Not covered.” This includes balconies or terraces that are not covered. Roof overhangs are not considered cover in this context.7
Areas such as crawl space, basement bays, external stairs and unusable roof areas are not taken into account calculating GFA. These are areas that are not usable floor plan levels.8
In valuation in accordance with the asset value method, these components of the building are included in the calculation as “special components”.
DIN 277 includes more detailed guidelines for the calculation of gross floor area, which must be taken into account in individual cases.